1. Field of the Invention
This invention relates to a dual plunger pump system for use in, for example, a flow-injection analyzer and a fluid analyzer used in a fluid chromatographic device.
2. Description of the Prior Art
Generally, fluid flowing through a fluid analyzer employed in a fluid chromatographic device should be supplied thereto without causing any pulsating flow in order to be measured with a high accuracy. Therefore, the conventional fluid analyzer of an old type has been provided with the so-called damper mechanism using air pressure. Recently, there has been proposed the dual plunger pump system of the latest type using two plungers which are alternately reciprocated in plunger cylinders for introducing the fluid into one conduit so as to prevent the pulsating flow of fluid. (Japanese Patent Application Public Disclosure SHO 56-98582(A) and Japanese Utility Model Registration Application Public Disclosure SHO 61-32950(A))
Also in a case of combining luminescent reagents or other reacting reagents with each other to be reacted in the conduit in the aforesaid fluid analyzer, the dual plunger pump system has been used for alternately introducing two kinds of reagents to be combined into one conduit by the reciprocations of the respective plungers in the pump. In this case, the smaller the amount of the fluid supplied by one reciprocating stroke of the plunger is, the more the efficiency of combining the reagents increases. Thus, there are being used a dual plunger pump system of the trace-quantity supplying type in which the reciprocating stroke of each plunger is made small.
In the trace-quantity supplying type dual plunger pump system as above, since the volume of the plunger cylinder per one reciprocating stroke of the plunger is small, the change of pressure in the conduit into which the fluid is fed is small, causing evolution of air bubbles tending to be adhered to the interior of a check valve used in the pump. The air bubbles have a function of absorbing the pressure produced by the reciprocating plunger, thereby preventing the fluid from being sent through the conduit.
In order to solve the problem noted above, there has been so far used a plunger pump system as shown in FIG. 6, in which a change valve 2 is connected to the discharge pipes 3a and 3b of plunger pumps 1a and 1b so that the discharge pipes 3a and 3b can be alternatively connected freely to either conflux passages 4a and 4b or scavenging-deaerating passages 5a and 5b. To the scavenging-deaerating passages 5a and 5b, there are connected high-volume manual suction pumps 6a and 6b so as to be manually operated for cleansing the interior of the plunger pumps 1a and 1b while removing the air bubbles in the plunger pumps at the beginning of operation.
As noted above, the conventional dual plunger pump system calls for the onerous works for scavenging and deaerating, which are manually performed at the outset each time different fluid samples are dealt with. The scavenging and deaerating works could not be automatized and have entailed a disadvantage such that the conventional dual plunger pump system cannot be applied to a fluid analyzer capable of dealing with a great quantity of fluid, which has appeared with progress in medical science.